Crankshafts



June 28, 1966 sEuLE ETAL I 3,257,865

CRANKSHAFTS Filed March 25, 1965 I 2 Sheets-Sheet 1 g 2 Sim/ nfers June 28, 1966 e. SEULEN ETAL 3,257,865

CRANKSHAFTS Filed March 25, 1963 2 Sheets-Sheet 2 k A lIlIIIll/llll1lll/ F ig..3

Jnvenlors MM 6 Claims. (61.14495) As known it has long been the established practice to provide crankshafts such as are used in internal combustion engines, with hardened bearing surfaces. Flame hardening and inductive hardening techniques have both been used for this purpose. In the past it has been the aim to provide the peripheral bearing surfaces with a hardened zone of even thickness and penetration. Steps have been taken to obviate irregularities in the hardened layer due to the presence of massive web members and their effect on the distribution of heat. The presence of the webs leads to an increased dissipation of heat in certain regions and, when hardening is performed by electroinductive means, the development of the magnetic field is likewise affected.

Modifications in the nature of the hardened zone have been permitted or even desired in the region of the reentrant angles, that is to say in the corners where .the bearing surfaces and the web members meet. According to the expected load particular attention is paid to the hardening of these corners, whereas in other cases it has been the aim to avoid hardening them.

The technique of surface hardening of both the crankpins and the main bearing surfaces of the shaft has been most successful. A method which has proved to be especially useful is that in which the crankshaft, or the United States Patent v the crankpin and the junctions with the webs.

bearing surfaces in question are arranged to rotate during I the process of heating and quenching. Although greater care in mounting and centring the crankshaft during the individual stages of the heating and hardening process must be observed than in methods in which the crankshaft is stationary and an inductor is arranged to embrace the bearing surface, the rotary method has the advantage that the crankshaft is less liable to distortion whilst being heated and quenched. Nevertheless, even in the rotary method the degree of distortion is still sufficiently great to necessitate subsequent straightening of the shaft Straightening is not a desirable operation, on the one hand, because it is an additional operation which incidentally calls for the greatest care in execution and, on the other, because straightening does not necessarily improve the treated shaft. It has been found that crankshafts which have been submitted to considerable straightening tend subsequently, at the operational temperatures in the engine, to distort again, thereby reducing the life of the hearings or of the shaft below that of a shaft which has been subjected to only a modest degree of straightening or which has not required straightening at all.

The known proposal inductively to reheat a crankshaft with hardened bearing surfaces in the region of the websand crankpins prior to straightening has not been a success in practice because this is a complicated operation to perform. Moreover, it could be applied only to fairly large crankshafts with webs of sufficient length to make such a heating process possible. Moreover, this step does not eliminate the necessity of straightening as such, but merely facilitates straightening or permits a modified method of straightening to be used instead of the classical method.

The object contemplated by the inventors is that of providing a crankshaft which exhibits a minimum degree Patented June 28, 1966 of distortion irrespectively of the method of hardening to which it has been subjected but particularly when the electro-inductive method has been employed, and which therefore does not require straightening after having been hardened and before being finish machined. According to the invention the problem is solved by providing the crankpins with a hardened layer which from the side remote from the crankshaft main axis increases in volume around the periphery to the side of the crankpin nearest the crankshaft main axis. The volume of the hardened layer is therefore intended to increase to a maximum where the crankpin surface faces the main crankshaft axis.- This increase in volume can be achieved either by increasing the penetration or the width of the hardened layer. Moreover, the depth and the width of the hardened zone may both increase towards the inside peripheral face of the crankpin in order to achieve the contemplated result. Hardening may alfect either only the crankpin as such or it may also involve the inside corner at the junction of the pin and the webs. .Moreover in the region of the outer shoulders hardening may be confined to the crankpins and on the inside hardening may embrace both stresses and/or the torsional stresses are a minimum.

In any case it is essential that the volume of the hard martensitic phase should be least on the side facing away from the crankshaft main axis and increase around the periphery to the side nearest the crankshaft mainaxis where its volume should be a maximum.

According to the invention the main bearing surfaces of the crankshaft should be evenly hardened all round as has in the past been conventional on'all the bearing surfaces of a crankshaft.

Surprisingly a crankshaft as proposed by the invention on which the hardening pattern is as above described, does not require to be straightened after it has been thus hardened. After a few trial hardenings it is quite easy for a person skilled in the art to adjust the variations in volume of the martensitic layer on crankpin diameters of any size in such a way that the distortion of the crankshaft is minimal- In the drawings:

FIG. 1 is a representation of a four-throw crankshaft,

shown partly in section;

FIG. 2 is a section taken on the line AA seen in the arrowed direction;

FIGS. 3 and 4 are axial sections of crankpins.

The crankpins are marked 1 to 4. 5 to 9 are the crankshaft main bearings. The partial section in the region of the crankpin 2 and main bearing 7 reveals that the hardened layer indicated by dotted lines uniformly surrounds the surface of the main bearing 7. However on the crankpin 2 the hardened layer is relatively thin at 11. On the side of the crankpin nearest the crankshaft axis 12 the hardened layer is indicated at 13 where it will be seen to be substantially thicker. As shown in FIG. 2, the thickness of the layer uniformly increases in thickness around the periphery. The same applies to crankpin 4. Nearest the main crankshaft axis 12 the hardened layer is particularly thick, whereas on the opposite side of the pin at 15 it is relatively thin. The other crankpins 1 and 3 are hardened in conformity with the same principle.

The hardened layer may extend into the re-entrant angles at the webs, as will be understood from FIG. 3. According to the invention the depth of penetration of the hardened layer may here also be non-uniform. In a further development of the invention the hardened layer adjacent the external circle 18 described by the revolving crankpin may extend only along the surface 20 of the The tranactual pin, whereas on the side facing the crankshaft axis the angles between the pin and the webs may likewise be hardened. The region of relatively shallow penetration, as shown in FIG. 4, does not extend into the webs, whereas at 19 the inside corners formed between pin and webs are also hardened. The point of transition where the hardened layer begins to extend into the junction between pin and web should be in a region where the stress reversals and/or torsional stresses are a minimum. In any case the essential point is that the volume of the hardened region should be greater on the side facing the crankshaft main axis 12 than on the side facing away from the crankshaft main axis adjacent the outside circle of gyration 18 of the pin. It is assumed that the forces of expansion generated by the increase in volume when the martensitic structure is formed will just compensate. In principle it is immaterial to the properties of the crankshaft which particular method is used for hardening the same. However, it is most convenient to use the inductive heating method, particularly the overall surface hardening method in which the pin rotates in relation to the induct-or which has the shape of a loop only partly embracing the pin. When after a number of revolutions of the pin exposed to such an inductor the pin has reached the required hardening temperature the inductor is shut down and the quenching medium is applied to the pin.

According to the invention the several crankpins are heated non-uniformly around their periphery according to a set programme in a manner counteracting distortion by generating a hardened layer which peripherally increases in depth and/or width i.e., in radial sectional area, to a maximum and then decreases again. An inductor which only partly embraces the revolving pin can be supplied with an effective power which varies in synchroni-sm with the rotation of the shaft. This power can be controlled by varying the excitation of the generator which provides the alternating current for the induction heating equipment.

Furthermore, in the electrical circuit of such induction heating equipment reactances may be provided either in the oscillating circuit itself or preceding the same. The power supplied to the inductor can then be controlled by varying the characteristic of the reactance. This can be-done for instance by providing movable cores or by varying the D .C. bias of the reactor core.

Another possibility of controlling the power consists in varying the inductive resistance of the inductor supply leads. This can be done by providing cores between the conductor branches which can be inserted or withdrawn in controllable manner.

Another method of controlling the power consists in changing the gap between the inductor and the treated surface periodically in synchronism with the rotation of the pin. The simplest arrangement is to control the direct electrical effect in functional dependence upon the rotation of the pin. For instance, it is already known to vary the power in dependence upon the angular position of the crankshaft.

However, other circuit and control arrangements which are already known in other connections could likewise be used. For instance, a master shaft could be provided. It is also possible to provide cammed discs. for generating the necessary motions of switch means or mechanical parts. Moreover, use can be made of cams, limit switches and like devices.

The simplest way of generating the hardening pattern required by the invention consists in increasing the thickness of the hardened layer around the peripheral surface and then decreasing it again. When this is done the width usually increases and decreases at the same time. The uniform increase and decrease in width of the hardened layer in the axial direction of the crankpin can be achieved with the same or similar means as those enumerated above.

In the description of the method of producing a crankshaft according to the invention it has been assumed that the crankshaft revolves during the heating and quenching operation because this is a method which already causes the least degree of distortion. Nevertheless, the method in which the crankshaft is stationary and is heated by an inductor completely embracing the same may likewise be used. The depth and width of the heated zone can then be controlled by keeping the power supply constant and by applying irregularly distributed laminated iron stacks to the periphery of the inductor in such manner that the induction effect rises peripherally on the crankpin to a maximum and then falls again.

What we claim is:

1. A steel crankshaft having hardened bearing surfaces including at least one crankpin having a hardened peripheral layer the volumes of which on the side of the pin facing away from the main axis of the crankshaft and on the side nearer to the said axis are inversely proportional to their distances from the crankshaft axis.

2. A steel crankshaft according to claim 1 in which the depth of the hardened layer is at a maximum nearest to the crankshaft axis and progressively lessens to a minimum at the zone furthest from the said axis.

3. A steel crankshaft according to claim 1' in which the width of the hardened layer in the axial direction of the pin is greater in the region which faces the crankshaft axis than in the region which faces away from said axis.

4. A steel crankshaft according to claim 1 in which the hardened layer extends into the re-entrant angles between the pin and the webs.

5. A steel crankshaft according to claim 1 in which the hardened layer in the crankshaft on the side of the pin facing away from the crankshaft axis does not extend into the webs of the shaft, but the layer extends gradually further into the crankpin and extends into the said webs in the peripheral region around the pin facing the crankshaft axis.

6. A steel crankshaft having main axially situated bearing surfaces each with a hardened peripheral layer of substantially uniform thickness and having crankpins each formed with a hardened peripheral layer extending round the whole periphery but progressively increasing and decreasing in-depth in that peripheral region of the pin which is nearer to the axis of the shaft and with a maximum thickness nearest to the said axis, the width of the layer viewed in the axial direction of the said pin being greater in the said region than in the region facing away from crankshaft axis and extending into the webs of the crankshaft so that the volumes of said layers respectively on the side of the pin facing away from the main axis of the crankshaft and on the side nearer to the said axis are inversely proportional to their distances from the crankshaft axis.

References Cited by the Examiner UNITED STATES PATENTS 1,112,087 9/1914 Patten 148-150 1,799,813 4/ 1931 Hinderliter 74-595 2,124,459 7/1938 Burgess 148-39 2,293,049 8/1942 Denneen et al. 148-150 2,365,394 12/1944 Criswell 74-595 2,590,546 3/1952 Kincaid et al 148-146 2,890,975 6/1959 Lenz 148-146 3,108,913 10/1963 Sommers 74-595 MILTON KAUFMAN, Primary Examiner. BROUGHTON G. DURHAM, Examiner. W. S. RATLIFF, Assistant Examiner. 

1. A STEEL CRANKSHAFT HAVING HARDENED BEARING SURFACES INCLUDING AT LEAST ONE CRANKPIN HAVING A HARDENED PERIPHERAL HAVING THE VOLUMES OF WHICH ON THE SIDE OF THE PIN FACING AWAY FROM THE MAIN AXIS OF THE CRANKSHAFT AND ON THE SIDE NEARER TO THE SAID AXIS ARE INVERSELY PROPORTIONAL TO THEIR DISTANCES FROM THE CRANKSHAFT AXIS. 